This invention relates to a computer system containing multiple storage subsystems, and more specifically, to a technique of migrating written data and a journal from one storage subsystem to another.
An amount of data handled in information systems of corporations has been increasing in recent years. Such data is managed by large-scale storage subsystems such as disk array. Corporations enhance availability of their information systems by backup a storage area (data volume). The backup enables the information systems to recover data even when data is damaged because of a failure in a storage subsystem or because of a virus, or when data is lost due to a misoperation by a user, or the like.
For example, JP 2004-252686 A discloses a backup and recovery technique by journaling. According to the technique of JP 2004-252686 A, “After journal data” is written in a copy of a data volume at a specific point in time (snapshot), and a storage subsystem can thus recover data that has been in storage at any point in the past subsequent to a creation of the snapshot. After journal data is data that is written in a data volume after a snapshot is taken. A common term for this technique is continuous data protection (CDP).
The technique disclosed in JP 2004-252686 A also enables a storage subsystem to recover data that has been in storage at any point in the past before the time when a snapshot of a data volume at a specific time point is taken by writing “Before journal data” back in the snapshot. Before journal data is data before update made to a data volume through data write.
In the following description, the term journal includes “After journal” and “Before journal”.
JP 2005-222110 A discloses a recovery technique with which data is recovered in a storage subsystem that is not one storing a journal. According to this technique, a first storage subsystem sends a Before journal and an After journal to a second storage subsystem, which recovers data using the received Before journal and After journal.
JP 10-508967 A discloses an inter-storage subsystem data migration technique. The technique disclosed in JP 10-508967 A shortens a time during which a system is shut down for data migration by having a destination storage subsystem perform a data migration process while the system is in operation.
Specifically, the destination storage subsystem is connected to a host computer and to a source storage subsystem. The destination storage subsystem copies data that is stored in a data volume in the source storage subsystem to a data volume in the destination storage subsystem. The destination storage subsystem does not stop accepting access requests from the host computer during the data copy process. In a case where data that is requested in an access request issued by the host computer is stored in the data volume of the destination storage subsystem, access to this data is granted.
In a case where data requested in the access request is not stored in the data volume of the destination storage subsystem, the destination storage subsystem copies the data requested in the access request from the data volume of the source storage subsystem to the data volume of the destination storage subsystem. Access to the data requested in the access request is then granted.
The technique disclosed in JP 10-508967 A thus allows a system to continue to operate during data migration.